Scalp-recorded evoked potentials permit sensitive, objective, and quantitative non-invasive examination of function in defined regions of the CNS. In recent years, they have become important clinical and research tools. At present, evoked potential evaluation of the auditory system is most successful on the brainstem and peripheral levels. Incomplete definition of the scalp-recorded activity, and uncertainties concerning proper electrode placements and referencing, have impeded auditory evoked potential (AEP) evaluation of auditory cortex. Recent studies provide basic data necessary for such development. They indicate that AEPs recorded over temporal scalp contain components produced in underlying auditory cortex and show how these components are best recorded and separated from concurrent activity originating elsewhere. These components display hemispheric differences consistent with the established anatomic and physiologic features of the auditory system and are sensitive monitors of acute and chronic CNS effects of several drugs and of subtle abnormalities in auditory pathways. They should be able to provide powerful non-invasive means for evaluating auditory cortex function. Achievement of this capability requires data concerning the dependence of these components on auditory cortex and on function elsewhere in the cortex. In order to fulfill these requirements, we will record from patients with focal cortical lesions involving auditory cortex or other cortical areas and from patients with focal cortical lesions involving auditory cortex or other cortical areas and from controls. We will use scalp, primarily temporal scalp, electrode placements, all referred to a balanced noncephalic reference electrode. Averaging and analysis will be performed off-line from digitized raw data. We will also record brainstem suditory evoked potentials (BAEPs) and perform audiometric studies. The control data should clearly define normal latencies and amplitudes of auditory cortex AEP components. The data from patients with focal cortical lesions should further establish the origins of these components, delineate their dependence on auditory cortex, and begin to establish their value in studying auditory cortex.